1. Field of the Invention
The present invention relates to a method for producing resin particles and a toner using the resin particles.
2. Description of the Prior Art
As for electrophotography, there are known various methods. Usually, these methods include the process of forming an electric latent image on a photoreceptor by the use of a photoconductive material and various means (an exposing process), the process of developing the latent image by the use of a toner to form a toner image, the process of transferring the toner image to a transfer material such as paper, and the process of heating or pressurizing the toner image by the use of a fixing roller to fix it onto the transfer material.
A toner for use in such electrophotography is produced by, for example, a grinding method, a polymerization method, or a spray drying method.
In the grinding method, a raw material containing a resin as a main component (hereinafter, simply referred to as a “resin”) and a coloring agent are kneaded at a temperature equal to or higher than the softening point of the resin, and then the resulting kneaded material is cooled and ground to obtain a toner (see, for example, Denshishasin Gakkai (ed.), “Densishashin no Kiso to Ohyo”, Corona Publishing Co., Ltd., pp. 482–486 (1988)). Such a grinding method is excellent in that a wide variety of materials can be used and therefore a toner can be produced relatively easily. On the other hand, however, the grinding method involves a drawback in that a toner obtained by this method tends to have great variations in shapes of particles, that is a particle size distribution is wide. As a result, electrification properties and fixing properties also vary greatly among toner particles, thereby lowering the reliability of the toner as a whole.
In the polymerization method, toner particles are produced by polymerizing a monomer that is a constituent of a target resin in a liquid phase or the like (see, for example, Japanese Patent Laid-open No. Hei 6-332257, page 2, lines 28 to 35). Such a polymerization method is excellent in that the obtained toner particles have a shape with a relatively high degree of sphericity (that is, a shape close to a geometrically perfect sphere). On the other hand, however, in the polymerization method there is a case where it is impossible to sufficiently reduce variations in particle diameter. Further, in the polymerization method, a range of choices of resin materials is narrow, and therefore there is a case where it is difficult to produce a toner having desired properties.
In the spray drying method, a material for use in producing a toner is dissolved in a solvent, and is then sprayed to obtain fine particles for a toner. Such a spray drying method is advantageous in that the grinding step as described above is not necessary. However, in the spray drying method, since the material is sprayed using high-pressure gas, it is difficult to precisely control conditions at the time of spraying the material. Therefore, it is difficult to produce toner particles having desired shape and size efficiently. Further, in the spray drying method, sprayed particles of the material have large variations in size, and therefore there are differences in their traveling speeds. As a result, there is a case where collision or agglomeration occurs between the sprayed particles before they are solidified, so that particles having various shapes are formed. This results in a case where the finally obtained toner particles have large variations in size and shape. As described above, since a toner obtained by the spray drying method has large variations in size and shape among toner particles, variations in electrification properties and fixing properties among the toner particles also become large, thereby lowering the reliability of the toner as a whole.
Further, such a conventional spray drying method has another problem in that hollow particles are likely to be produced, because a material for use in producing a toner dissolved in a solvent is usually sprayed into an atmosphere with high temperature so that the solvent is Volatilized rapidly.